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Discussion Starter #1
My Stealth has had a strange issue for a while that I can't track down. At lower RPMs under load the car consistently shakes, and if I get in to boost it will stutter, buck and pop. The car runs beautifully under all other conditions so this one has left me scratching my head for a while. Back in august the car got new plugs, a new rebuilt ECU, and a full 60k service as well as upper engine seals including head gaskets and valve stem seals. I've put about 1000 miles on it since then and this problem is still hanging around. I'll attach my log starting just moments before the stutter happens and I let off the throttle. The log shows knock at that moment so I don't know what to think. Any help or opinions is appreciated.


Log: Log 1-20.csv



Quick picture of the log at the time of stutter (Right when the knock starts):
286028
 

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I assume you are using torque to datalog, and based on what i am seeing, you are using a bluetooth OBD2 adapter? It looks like your OBD2 adapter is way too slow for the logging interval and number of PIDs you are logging. Basically you are only getting new values every 3 seconds, which is quite slow (you can see this based on values being duplicated repeatedly). Difficult to discern what is happening in real time with this logging speed. The screenshot you showed therefore only has 3 data points. For starters you can remove the two fuel trim columns that never change, along with the O2 sensor columns except voltage on bank 1 and bank 2 sensor 1 (upstream primary O2s). You can also remove speed from 2nd to last column. Removing unnecessary PIDs will speed up the logging interval you can achieve even with a slow OBD2 transmitter.

In any case, can you elaborate on the conditions when the car does run normal? You said it has the issue under low load and under boost... what is left, idle? The popping and stuttering is probably a fuel or spark issue, just need to know exactly when it does/does not happen to try and narrow down causes.

Also, any relevant mods?
 

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Discussion Starter #3
I assume you are using torque to datalog, and based on what i am seeing, you are using a bluetooth OBD2 adapter? It looks like your OBD2 adapter is way too slow for the logging interval and number of PIDs you are logging. Basically you are only getting new values every 3 seconds, which is quite slow (you can see this based on values being duplicated repeatedly). Difficult to discern what is happening in real time with this logging speed. The screenshot you showed therefore only has 3 data points. For starters you can remove the two fuel trim columns that never change, along with the O2 sensor columns except voltage on bank 1 and bank 2 sensor 1 (upstream primary O2s). You can also remove speed from 2nd to last column. Removing unnecessary PIDs will speed up the logging interval you can achieve even with a slow OBD2 transmitter.

In any case, can you elaborate on the conditions when the car does run normal? You said it has the issue under low load and under boost... what is left, idle? The popping and stuttering is probably a fuel or spark issue, just need to know exactly when it does/does not happen to try and narrow down causes.

Also, any relevant mods?
I am using torque with a USB adapter set to update about 4 times a second. Look at the device time in the furthest left column to see how quickly it is updating. The link to the rest of the log is available in my above post but I'll post it again here (Log 1-20.csv).

I'm sorry for my poor description of the problem, it's rather hard to explain. The car runs perfectly at idle and perfectly under any load at any RPM at low speeds (i.e first and second gear). The car runs beautifully at high RPMs at higher speeds in gears 3 - 5, but if you let the RPM drop below 2500 and give the car more than half throttle it stutters, bucks and shakes. I can even hear a sort of popping sound, not really a backfire but hard to describe. The problem seems even worse if you manage to get in to boost in those low RPMS. The only mods I've done are full cat deletes, EGR delete, and an HKS bov, other than that the car is stock with 44,000 miles.
 

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Yes, i can see that you have logging interval set to 0.25 seconds. However, the fact that you are getting so many duplicate values in a row means that there is a bottlenneck somewhere; usually it is the OBD2 adapter. If you are using USB, it could be an incorrect setting/configuration. When you open torque how many PIDs/sec does it show you are getting? Should be under settings somewhere. Basically, you should be seeing a new value every 0.25 seconds (no duplicate rows) if your adapter/device are capable of supporting the 0.25 second logging interval. I saw the exact same thing as you when using bluetooth with ~15-30 pids/sec, but once i went to USB and configured it properly, i was getting over 200. Do you real-time gauges refresh "instantly" or is there some delay?

Sorry didnt see the link to the full log. The same duplicate value issue is in the entire log from what i saw.

So, lower RPM in higher gears when throttle > 50%. But same conditions in gears 1 and 2 no issue? Strange, the only thing higher gears would do is more load... the ECU doesn't know what gear you are in. I assume you have boost leak tested (sorry, but always the first suggestion on a turbo car)?

If you capture a log with a faster refresh rate of the logged parameters when the issue occurs we might be able to figure something out, but nothing seems immedaitely obvious to me if it doesnt do it in 1st and 2nd under the same conditions.
 

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Discussion Starter #5
Yes, i can see that you have logging interval set to 0.25 seconds. However, the fact that you are getting so many duplicate values in a row means that there is a bottlenneck somewhere; usually it is the OBD2 adapter. If you are using USB, it could be an incorrect setting/configuration. When you open torque how many PIDs/sec does it show you are getting? Should be under settings somewhere. Basically, you should be seeing a new value every 0.25 seconds (no duplicate rows) if your adapter/device are capable of supporting the 0.25 second logging interval. I saw the exact same thing as you when using bluetooth with ~15-30 pids/sec, but once i went to USB and configured it properly, i was getting over 200. Do you real-time gauges refresh "instantly" or is there some delay?

Sorry didnt see the link to the full log. The same duplicate value issue is in the entire log from what i saw.

So, lower RPM in higher gears when throttle > 50%. But same conditions in gears 1 and 2 no issue? Strange, the only thing higher gears would do is more load... the ECU doesn't know what gear you are in. I assume you have boost leak tested (sorry, but always the first suggestion on a turbo car)?

If you capture a log with a faster refresh rate of the logged parameters when the issue occurs we might be able to figure something out, but nothing seems immedaitely obvious to me if it doesnt do it in 1st and 2nd under the same conditions.
Hmmm. I'll check my settings in the app for the OBD adapter. And you would be correct in the assumption that it seems to be load dependent. It almost feels as if the car is lugging and doesn't have the power to pull at those lower RPMs in 3rd - 5th gear. I've done a boost leak check, I couldn't get the air to stop escaping though the oil cap even when plugging the pcv hoses like recommended. There was only one slight leak on the BOV at 10psi of pressure. I plan to get with HKS about a replacement there. You think a tiny boost leak would cause such a problem?
 

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Following up on the load theory -

1. Do you have any steep hills? Can you test going down a steep hill in the conditions that produce the problem to see if it still happens? (hill reducing load). Or, up a steep hill in a lower gear (hill increasing load) to see if it happens?

2. Also, does the car run fine at higher RPMs in 3rd-5th? It's just the low RPMs that are the problem?

I don't think a small boost leak could cause inconsistent problems across gears like that. It also should not be closed loop issue (O2 sensors) because that should not be happening at high load/throttle input. Is the boost pressure in your log accurate? 10.6 psi at 2200 rpm, 78% throttle, right before problem occured?

Have you set base timing and checked with a timing light?
 

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Just posting my 2 cents. I had this happen to my wife's Mazdaspeed 6 when I had rebuilt the head. It ran fine, but when putting your foot down at all (even a little) it would buck and pop. Fearing I had messed up the timing, I started to dismantle the top part of the engine and I had found a faulty ground for my coils. Basically it could provide the spark for no load, but any time it would try to advance the timing, the coil would fail due to the ground.

Hope this helps!
 

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Discussion Starter #9
I'm beginning to sound like a broken record at this point, but this is exactly what my VR4 was doing when the fuel pump voltage relay went bad. The bypass fix is like $5 worth of parts and is relatively simple to do, here is a link for it on stealth316..
I just did the bypass and it has solved 80% of the stuttering. Thank you so much for that suggestion! There is still some strangeness occurring every now and again, but I think that may be due to my ECS controller starting to go out. It acts moody occasionally and the tour/sport lights flash, but if I restart the car it works fine. The car has developed some light popping at idle since I last posted also. I'm hoping it's just some bad gas and will pass with time because I don't have any other issues otherwise.
 

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I just did the bypass and it has solved 80% of the stuttering. Thank you so much for that suggestion! There is still some strangeness occurring every now and again, but I think that may be due to my ECS controller starting to go out. It acts moody occasionally and the tour/sport lights flash, but if I restart the car it works fine. The car has developed some light popping at idle since I last posted also. I'm hoping it's just some bad gas and will pass with time because I don't have any other issues otherwise.
ECS can definitely cause issues similar to ECU symptoms. Its fine to run with it unplugged, i have been for years.
 

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Discussion Starter #11
ECS can definitely cause issues similar to ECU symptoms. Its fine to run with it unplugged, i have been for years.
I would, but I like the nice smooth ride I get in tour mode, haha. I'll probably replace the caps on the ECS board soon.
 

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There is still some strangeness occurring every now and again, but I think that may be due to my ECS controller starting to go out. It acts moody occasionally and the tour/sport lights flash, but if I restart the car it works fine.
This symptom is not necessarily a symptom of a bad ECS controller but rather the ECS module telling you it has detected a problem and the most common cause for what your describing is broken Strut wire cap harnesses wires where the harness plugs into the top of the Front struts. Start by reseating all the ECS plugs.

If an ECS module really fails you usually dont get any lights at all. And in this point the ECS module shares the TPS electrical feed with the ECU.. so it is possible (but not very often) for the ECS unit to fail and in the process screw up the voltage readings on the TPS feed to the ECU - if it does this its going to cause throttle problems either at idle or under acceleration. If you disconnect the ECS module and nothing changes throttle wise - it is not the ECS unit.

duke3k
 

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I would, but I like the nice smooth ride I get in tour mode, haha. I'll probably replace the caps on the ECS board soon.
I am fairly certain that unplugging the ECS defaults to tour mode, but i could have that backwards... I know when there is an issue and you have both blinking lights it defaults to sport. That's how i remember it, but it has been years since i had mine in. But my car doesnt seem like it rides in the sport setting with it unplugged.
 

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Discussion Starter #14
This symptom is not necessarily a symptom of a bad ECS controller but rather the ECS module telling you it has detected a problem and the most common cause for what your describing is broken Strut wire cap harnesses wires where the harness plugs into the top of the Front struts. Start by reseating all the ECS plugs.

If an ECS module really fails you usually dont get any lights at all. And in this point the ECS module shares the TPS electrical feed with the ECU.. so it is possible (but not very often) for the ECS unit to fail and in the process screw up the voltage readings on the TPS feed to the ECU - if it does this its going to cause throttle problems either at idle or under acceleration. If you disconnect the ECS module and nothing changes throttle wise - it is not the ECS unit.

duke3k
Hmmm, I'll check those cap harnesses out further. I had looked them over once before when I started having issues, but I just checked for obvious frayed or broken connections. Thanks for the advice! I do plan to purchase one of your custom ECS controllers should my unit ever go out.
 

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Discussion Starter #15
I am fairly certain that unplugging the ECS defaults to tour mode, but i could have that backwards... I know when there is an issue and you have both blinking lights it defaults to sport. That's how i remember it, but it has been years since i had mine in. But my car doesnt seem like it rides in the sport setting with it unplugged.
It defaults to sport since the struts default to their firmest position with the absence of the ECS controller. I've driven with it unplugged a few times.
 

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I am fairly certain that unplugging the ECS defaults to tour mode,
Sorry guys but if you unplug the ECS controller there is no “default” mode. The struts will be in whatever mode they were last left in just before the controller was last on , working and unplugged.

If the ECS controller has failed and is still plugged in then essentially same answer as above - there is no default mode in this case - struts will still be stuck in the same mode they were in just before the controller failed

The default mode only applies if the ECS controller is working and it detects a fault somewhere else in the system. If you see blinking Sport& tour light then this is the case and your ECS controller will try and put all four struts In Sport mode. If one of the struts is bad wiring etc it won’t be able to.

Also in the case where you fresh start the car and you see no blinking lights and only the Tour light comes on and is solid. Then (a) you know your ECS controller is working and (b) that all four of your struts have been successfully command into Soft mode. If you now turn off your car and unplug the ECS unit - now your struts will be permantly in soft mode.
 

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Discussion Starter #17
Sorry guys but if you unplug the ECS controller there is no “default” mode. The struts will be in whatever mode they were last left in just before the controller was last on , working and unplugged.

If the ECS controller has failed and is still plugged in then essentially same answer as above - there is no default mode in this case - struts will still be stick in the same mode they were in just before the controller failez

The default mode only applies if the ECS controller is working and it detects a fault somewhere else in the system. If you see blinking Sport& tour light then this is the case and your ECS controller will try and put all four struts In Sport mode. If one of the struts is bad wiring etc it won’t be able to.

Also in the case where you fresh start the car and you see no blinking lights and only the Tour light comes on and is solid. Then (a) you know your ECS controller is working and (b) that all four of your struts have been successfully command into Soft mode. If you now turn off your car and unplug the ECS unit - now your struts will be permantly in soft mode.
Huh, I never knew that. I thought the ECS controller actively controlled the struts to make minor adjustments while in tour mode so without the input from the controller they would default to hard. I'm not questioning your expertise here. I know for a fact you've done your research considering you've literally made your own controller, lol. That's very good information to know.... I think I might just set my car to tour mode and unplug it in the future.
 

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I thought the ECS controller actively controlled the struts to make minor adjustments while in tour mode so without the input from the controller they would default to hard.
The first part of your statement is correct ie. in Tour mode the Ecs controller does automatically change the struts to soft , medium or hard as needed. However if the controller fails there’s nothing to perform the logic for what command to send and more importantly the controller is responsible for energizing the electrical motors inside the struts. If it’s failed or unplugged the struts have nothing to power them. They will be stuck in whatever mode they were last in. Make sense?
 
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